The problems associated with statically charged air particles in the vicinity of sensitive manufacturing processes and sensitive work pieces are not new. The build up of static charges on sensitive electronic components may lead to severe damage of those components. The localized static charges themselves may damage or degrade particularly sensitive electronics. More importantly, electrotatic forces on electronics surfaces create an electric field that attracts contaminants carried by the air. Dust particles in the air may be so small that they are little affected by gravity, but rather settleing of the dust particles is brought about by electrostatic forces.
Air ionizing apparatus are well known to dramatically reduce the deposition rate of small dust particles, by propelling ions into the air surrounding a work area to neutralize charged materials present. Partridge, U.S. Pat. No. 5,055,963 (issued Oct. 8, 1991) describes a housing with generally open inlet and outlet passages, and a fan and electrodes mounted inside the housing. The fan creates an air flow that pulls room-air through an opening in the back of the housing, and after being ionized the air is propelled out an opening in the front of the housing. Le Vantine, U.S. Pat. No. 4,635,161 (issued Jan. 6, 1987) discloses a device having dual air supplies that lead to a positive or negative electrode, and the ionized air is mixed in a vortex chamber. The ionized air is then propelled out the front of the device through small air jets.
Other prior art devices include air ionizing rings where high pressure air is supplied through a small gap in the ring, and flows through the ring past electrodes into the workstation. These air-ionizing rings are typically precision machined parts to provide the small gap and surfaces around which the air flows. Shims may be required to control the dimensions of the small gap.
Although the prior art devices have proven generally suitable for their intended purposes, they possess inherent deficiencies which detract from their overall effectiveness and desirability. Ionization takes place at the sharp pointed end of the electrode where an intense electric field develops called a corona. During ionization, the electrode tends to accumulate aluminum nitrate at the corona from moisture contained in the room air. Over time, this leads to a decreased output of ionized gas particles, and eventually the electrode must be cleaned or replaced. Also, contaminants on the electrode tips themselves tend to be discharged into the air during the ionization event.
It is recognized that it is important to produce a balanced number of positive and negative ions through properly functioning electrodes, to avoid actually contributing to the problem of static discharge in the vicinity of workpieces. Partridge disclosed wiring for a self-balancing circuit, where if the output of one charge changes relative to the other, the circuit re-equalizes itself by changing the output of the opposite charge. Other prior art devices have included conductive sensors to indicate when maintenance of an electrode is required.
The designs of the prior art devices also tend to interfere with the room air flow and lighting around the workstation. In clean room environments where electronics manufacturing typically takes place, filtered air and lighting are provided from overhead. The prior art devices tend to develop a turbulent air flow surrounding them, and cast a shadow across the workstation. The turbulent flow of air may also have the undesired effect of increasing combination of the positive and negative ions before they reach the electronics surface to be neutralized.